Multiplexing



Patented Oct. 13, 1942 MULTIPLEXIN G Harold 0. Peterson, Riverhead, N. YJ, assignor to Radio Corporation of America, a corporation of Delaware Application June 19, 1940, Serial No. 341,285

23 Claims.

This invention relates to multiplex signaling. An object of the invention is to provide an improved frequency modulation m'ultiplex system especially useful for high quality broadcasting, facsimile, and tone or code signaling.

Another general object is to provide a multiplex circuit especially adapted for multiplexing a plurality of high quality broadcasting channels upon a radio relay circuit. In effecting tliislatter object, according to this invention, frequency modulationis applied to a transmitter capable of handling a band width of, for example, eight megacycles for ten high quality channels. With such a radiocircuit modulation frequencies up'to about three megacycles may readily be accommodated.

Further in this connection, the band of possible modulating frequencies is divided into ten parts to accommodate frequency modulation at ten different sub-carrier frequencies. Each of these sub-carrier frequencies is in turn frequency modulated by the high quality broadcast program material. In this connection each subcarrier is frequency modulated with audio frequencies between about 30 cycles and inc. Since the noise which results upon demodulation of one of these sub-carrier channels will vary in proportion to audio frequency, Dre-emphasis and de-emphasis may be used in the same manner as is now used on, for example, the sound channel of the Empire State television station.

In considering the noise characteristics further, it is apparent that the higher frequency subcarrier channels will tend to have more noise in themthan the lower frequency sub-carriers. To overcome this tendency is a further object of this invention. It is carried out by the use of different band widths for the different sub-carrier channels so that more deviation will be used for the higher sub-carrier frequencies. A-desirable relationship would be to have the sub-carrier channel width proportional to the sub-carrier fre.-.

quency. With such a division of the frequency band the signal-to-noise ratio in each sub-carrier channel will be approximately equal.

Assuming that the main transmitted carrier is modulated with frequencies up to about 3000 k. c. and that a deviation of up to about 3000 k. c. can be-used for this frequency modulation of the main transmitter carrier, ten channels can I be set up as follows:

Frequency and Channel number width glaring;

Kilocyclea Kilocyclu 3 so 240 110 335 .470 220 600 e10 020 440 1,300 000 1,780 are 2,550

amount equal to 300 k. c. ofdeviation. This should result in a maximum deviation of 3000 k..c. Each of the sub-carriers would in turn be frequency modulated by an amount depending upon the band widths of the various channels as indicated above. The maximum deviation of each sub-carrier may be 0.3 times its corresponding band width.

By another arrangement, equal. sub-carrier band widths may be assigned to each channel, but

the higher frequency sub-carriers should be made Fre- Deviation of Channel quency main carrier Channel number b5513 or by each carrier carrier Ki eta Kiloci/du Kitocycies' 150 125 107 so 176 150 60 225 193 50 275 236 60 325 279 50 376 822 60 425 364 v 50 476 407 50 525 450 60 676 492 In the foregoing system each sub-carrier may be frequency modulated by the program material a maximum deviation of 15 1:. c.

Each of these sub-carriers would in turn fre- 4 quency modulate the main carrier by an amount Also, in carrying out this invention, phase modulation may be employed to advantage.

For example, if a crystal controlled oscillator followed by frequency multipliers is provided, any phase modulation of the oscillator would appear in the output circuit multiplied by the amount of frequency multiplication. For example, consider a crystal controlled transmitter having a final output frequency eighteen times the crystal frequency. Any phase modulation of the crystal frequency would be eighteen times as greatin the output. If we assume a phase modulation of one radian deviationat crystal frequency; the output would be modulated to a deviation of'eighteen radians. If this deviation is evenly divided between eleven fil-' ter channels each channel can be allowed .18/l1=1.63 radians. Since frequency deviation is the product of phase deviation times modulating frequency we would obtain the. following distribution of deviations for a standard filter Actually, there is a certain random effect which allows a somewhat greater deviation per channel without danger of overswing because the probability is that all channels will not swing one direction in phase.

Now if we take the above figures and assume a 180 ft. tower at New Brunswick, New Jersey,

for example, a transmitter output of four watts,

and parabolic antennas having 100 square feet cies.

a signal to'random noise ratio of about 65 db. for a signaling channel employing band pass filters 100 cycles wide may be obtained in such a radio link.

Further description of the present invention will be given with the aid of the accompanying drawings.

Figures land 2 illustrate some of the principles involved in the noise characteristics of a frequency 'modulated signal. Figure 3 shows a transmitter in which the main carrier frequency of the transmitter is frequency modulated by an equal amount by each of several sub-carriers. These sub-carriers are in turn frequency modulated by various deviations, said deviations increasing proportional to the sub-carrier frequencies; The object is to produce a system in whichthe signal-to-noise ratio will be equal in each of the various channels. In Figure 4 is shown another arrangement whereby the same objective is accomplished. In this case the main carrier frequency is frequency modulated by each of several sub-carriers in an amount which increases proportional to the sub-carrier frequen- Each sub-carrier frequency is in turn modulated by a fixed amount of deviation. Figure 5 shows a receiving'system that could be used for receiving this type of multiplex signal.

Figures 6 and 7 illustrate terminals involving some of the points in greater detail. 1 The frequencies indicated are merely for the purpose of illustration. Figures 8 and 9 show in block diagram form, arrangements of apparatus for carput varies over the frequency band and is proportional to the demodulated output frequencies.

. This is thoroughly described in a paper by M. G.

Crosby, entitled Frequency Modulation Noise Characteristics," which appeared in the I. R. E. Proceedings, vol. 25, No. 4, April 1937, pages 472-; 514, a v

In Figure 1, let 03 represent the unmodulated carrier received by a frequency, modulation receiver. Let BD represent a noise voltage at some frequency in the spectrum. Now if the noise vector ED is at a frequency different than the carrier frequency 03 we may represent vector ZBD as rotating about point B. It will be noted then that the resultant vector will oscillate back and forth between extremes 0A and 0C. In other words, the resultant will be phase modulated by the noise and the phase modulation will amount to a deviation equal to angle BOC also represented as in Figure 1-.

Another relationship in frequency modulation is that the frequency deviation is equalto the 7 product of the phase deviation multiplied by the apertures at N. B. and N. Y., it can be shown that modulation frequency; consequently, when there is greater frequency difference between the frequencies of the carrier vector OB and the noise vector IBD, the resulting modulation will correspond to a greater frequency deviation. Therefore, the noise output of the receiver will also be greater because the output of a frequency modulation receiver is proportional to the frequency deviation. This relationship between output noise voltage and demodulated frequency is also shown in Figure 2.

In Figure 3 is shown a transmitter I! with assume a carrier frequency of 500,000 k. c. This transmitter feeds antenna 20 througha transmission line l3. Antenna 20 may be a directive antenna such as a parabolic or a horn antenna. Transmitter l8 includes a frequency modulator so that the carrier frequency may be modulated by the voltage developed in load circuit resistor It. For instance, the carrier frequency of transmitter It may be frequency modulated over a range of plus or minus 1000 k. c. (1000 k. c. deviation). This frequency modulation of the main transmitter l8 may occur at various sub-carrier frequencies. These sub-carrier frequencies are generated in units 6, I, 8, 9 and I0, each of which is in turn modulated by the signal it is desired to transmit, thus various types of program material may,for example, be introduced through input circuits I, 2, 3, 4 and 5.

incoming carrier frequency. From here the signal goes into a heterodyne detector 44 where it is combined with energy from an oscillator The various sub-carrier frequencies ar impressed on the grids of vacuum tubes II, l2, l3, l4 and I5, all of which feed output into the modulator of transmitter l8. As an example, the various sub-carriers chosen are 120 k. c., 172 k. c., 240 k. c., 335 k. c. and-470 k. 0. Transmitter I8 is frequency modulated an equal amount by each of these sub-carrier frequencies. As an' example, each of these sub-carrier frequencies may impress 10 volts upon the grids of tubes II, l2, l3, l4 and I5.

Because of the noise relationship above mentioned, the 120 k. c. sub-carrier will appear to have a better signal-to-noise ratio in the receiver output than will the 470 k. c. sub-carrier. Another principle in frequency modulation is that the signal-to-noise ratio is proportional to the ratio of frequency deviation to modulation frequency; therefore, the overall signal-to-noise ratio can be equalized by using more deviation on the higher sub-carrier frequencies.

We may, for instance, assume maximum modulation frequencies of 15 k. c. on each of the channels I, 2, 3, 4 and 5. We may then, for instance, adjust, the various sub-carrier generators so that they ar frequency modulated by an amount which is proportional to their relative sub-carrier frequencies. Thus, we will impress 40 k. c. deviation on the 240 k. c. subcarrier and k. c. deviation on the 120 k. c. sub-carrier and other deviations on the other sub-carriers as indicated in Figure 3.

In Figure; it is assumed that each of the sub-carrier generators 26, 21, 28, 29 and 30 are modulated by equal amounts. For example, the various program channels 2l,'22, 23, 24 and 25 are caused to frequencymodulate the various sub-carriers each by a deviation amounting to 25 k. c. The main transmitter 38 is frequency modulated by all of the sub-carriers through vacuum tubes 3|, 32, 3-3, 34 and 35 coupled to the transmitter through-lead circuit resistor 38 and coupling condenser 31. As is indicated by the grid voltages to tubes 3|, 32, 33, 34 and 35 the higher sub-carrier frequencies are caused tomodulated an equal amount by each of several 1 r so 43 to produce an intermediate frequency which is passed through selectorcircuit 46, amplifier 41, limiter 43, and frequency modulation discriminator anddetector 43. In the output of 43 the signal appears in the form of the various frequency modulated sub-carriers. One of the sub-carrier frequencies is selected by each of the selector circuits 50, I5, 60, 83 and 10 which are followed by amplifiers SI, 56, ll. 43 and II. Fromthe amplifiers the signal passes into limiters 52, I1, 62, 61 and 12 which feed discriminator-detector circuits'53, 53, 63, i8 and 13 the outputs of which are represented at 34, 59, 84, 39 and 14. The original signals are reproduced in these output circuits.

As a further refinement and improvement in the signal-to-noise ratio the inputs in the-various channels may be pre-emphasized so as to impress more frequency deviation upon the subcarrier generators for the hi her signal frequencies. The original balance may then be taken care of by de-emphasis circuits in the various receiver outputs of Figure 5.

'. Whilst Figure 3 shows the main carrier to be sub-carriers, the sub-carriers be frequency modulated by various amounts proportional to subcarrler frequency and Figure 4 shows the main carrier to be modulated by various amounts proportional to sub-carrier frequency and the subcarriers in turn frequency modulated in equal amounts, itfshould be understood that similar results may also be obtained by a system which combines these two characteristics. For instance, the signals .can be caused to modulate The relay system may be used in long distance circuits in various ways. For example, waves of a length between 15 and meters, amplitude or phase modulated, may be transmitted from England and other far off points to Riverhead, Long Island. From Riverhead, the waves may be demodulated and retransmitted via the ultra short waverelay system described above to New York city, Conversely, a plurality of messages may be sent from New York city by way of the-relay system herein described to Rocky Point, Long Island, and there converted and demodulated for retransmission over long distance circuits on wave lengths above 15 meters to distant points.

Figure 6 illustrates the terminal at a receivingstation such as Riverhead, Long Island, whilst Figure 7 illustrates the New York terminal for the signals coming via u-Jt-f radio relay from Riverhead. With slight modifications, Figure 6 could serve to illustrate the New York-terminal for signals outgoing to control a transmitting station such as Rocky Point, Long Island, and Figure '7 with slight modifications could represent the terminal at the transmitting station.

In Figure 6 we have receiving antennas for the point-to-point frequencies at la, 2a, 3a, 4a,!a,

' as 425 cycles, 595 cycles, and 765 cycles.

8a, and la. These antennas may be of a directive type such as the fishbone or the rhombic antenna and they may be designed for receiving on different frequencies and from different directions. Also, each may actually be in the form of three antennas used ina diversity receiving system.

8a, 9a, ia, iia, Ila, i3a and Ma represent receivers for the point-to-point frequencies between approximately 3 mc. and 30 me. We may, in cases 8a, 9a, ifla'and Ila use a standard diversity telegraph receiver. In this receiver the incoming signal is caused to amplitude modulate practically 100%, local tone frequencies. These locally generated tones are represented in Fig. 6

ceiver #8a may be tuned to a signal from London, receiver #911 to a signal from Italy, and receiver #iila to a signal from San Francisco. The outputs of these three receivers pass through bandpass filters ia, [6a andi'ia into a frequency modulated sub-carrier generator 2ia in which they are caused to frequency modulate a source of 100 k. c, sub-carrier.

A maximum deviation of k. c. is indicated for the sub-carrier generator 2ia. It would be advisable to have higher deviation on the higher tone frequencies so that the overall signal-tonoise ratio would be the same on each channel. Thus, the deviation caused by the 765 cycle tone would be greater than the deviation'caused by the 425 cycle tone by a factor of 765 divided by As illustrated, antenna 4a and receiver iia re- .ceive a broadcast programwhich may include voice and music. This material is caused to frequency modulate sub-carrier generator 22a.

Antenna 5a and receiver l2a receives another telegraph circuit which is passed through bandpass filter iBa to frequency modulated sub-carrier generator 23a. Receivers l3a and a are shown to be receiving frequency shift facsimile signals, one of them being a tone of 3000 cycles with a deviation of 800 cycles and the other being a tone of 5000 cycles with a deviation of 1300 cycles. These are passed through band filters Ilia and 2011 respectively and together with the telegraph signal from filter i8a frequency modu-' late the sub-carrier generator 23a.

The frequency modulated sub-carriers from generators Zia, 22a and 2311 are caused to frequency modulate a uh transmitter 24a which feeds through transmission line 25a to antenna 2611. 200 k. c. sub-carrier is greater than that on the 100 k. c. sub-carrier and the deviation on the 300 k. c. carrier is still greater. As the deviation is made proportional to the sub-carrier frequency, the system might, as a matter of fact, be considered a phase modulation system since in phase modulation the frequency deviation is proportional to the modulation frequency.

In Figure '7 the 500 me. frequency modulated or phase modulated carrier is received on antenna 21b and conducted through transmission line 28b to a selective circuit 29b from which it goes to a converter 30b where it is combined with the frequency from a local oscillator 3ib. The intermediate frequency is selected in circuit 32b, amplified and'limited in circuit 33b, and demodulated in the discriminator and detector circuit llb. In the output of 34b we have the original sub-carrier frequencies which are selected by circuits 35b, 36b and 31b, amplified by 38b, 39b andlilb, limited by limiters lib, 42b and 43b, and demodulated by discriminator-detector circuits b, llb and b. x

In the-output of b we have the three-tone telegraph signals which are selected by filters 41b,- 48b and 49b and passed on to utilization circuits 50b, il b and 52b.

In the output of 45b we have the program modulation which is passed on to utilization circuit no.

In the output of 46b we have the tone telegraph signal which was received by receiver ilb. This is selected by filter 54b and transferred to the utilization circuit 63b. The two facsimile circuits are selected by filters 55b and "b, amplifled by amplifiers 51b and 58b, limited in "b and 60b, and demodulated in discriminator-detector circuits Gib and 62b from which they are transferred to utilization circuits 64b and "D. It will As indicated, the deviation on the be noted that in the case of the facsimile signal we have frequency modulation of a tone which in turn frequency modulates a sub-carrier. which in turn frequency modulates an ultra high frequency transmitter carrier.

It should, of course, be understood that a larger number of channels can be impressed upon any one of the sub-carriers shown. In general, it will be convenient to impress upon one sub-carrier approximately the number of channels that are now carried by a high quality telephone line.

In the case of the circuits going from the central oflice to the transmitting station we would substitute forthe receivers 8a, 9a, Ilia, lic, Ila, i3a and Ma of Figure 6 the original sources of signalat the central ofilce. In Figure 7 the utilization circuits 50b, Bib, 52b, 53b and 63b might be the tone keyers or modulators of the transmitters. In th case of the facsimile signals it would not be necessary to demodulate them at the transmitting station and the outputs of selective circuits 55 and 56 would go directly to the transmitter modulators.

These examples will serve to illustrate how systems may be set up. It will be appreciated that the number of various combinations possible can be very great without departing from the scope of this invention.

The use of phase modulation on an ultra high frequency circuit for the control of communications transmitter and receivers is shown in Figures 8 and 9. In Figure 8 each of the usual audio frequency filter bands is allowed to phase modulate the crystal frequency of the transmitter. The crystal frequency and its phase modulation would be multiplied together in the following multiplier stages. Equivalent frequency deviations have heretofore been given for a typical example. In practice, deviations greater or less than the amounts shown in this example may be used.

In Figure 8 we have tone generators ic, 2c and 30 which are modulated through keying devices 40, 5c and to feeding bandpass filters lo, and 9c. The outputs of these bandpass filters are combined to operate a phase modulator iiic wherein the carrier from oscillator lie is phase modulated in accordance with the various tones coming through filters 1c, 8c and 9c. The phase modulated carrier coming out of I00 is applied to the input of a series of amplifier-multiplier stages He in the manner well known to the transmitter art. The output of amplifier-multiplier i2c passes if frequency increases the current in detector A' decreases whilst the current in detector B increases and if the frequency decreases the re-' verse is true. Typical arrangements of this nature for phase modulation and for frequency modulation reception are more specifically described in Seeley Patent 2,121,103 and Crosby Patents 2,071,113 and 2,060,611. 7

Thus, the output of detector unit 220 is in the form of the original tone frequencies which may be separated off in bandpass filters 23c, 24c and 250 which connect to utilization circuits 26c, 21c and 280.

In Figures 8 and 9, I have shown only three channels but it would obviously be possible to use this principle for a considerably larger number'of channels, such as eleven or more.

It will be noted that since the phase deviation used by each channel is substantially equal, the signal-to-noise ratio realized in the various channels will be substantially equal.

Method and apparatus for applying audio or signal frequency pre-emphasis and de-emphasis are described in Hansell Patent 2,179,182 and Seeley Patent 2,007,985. As already stated, such pre-emphasis and de-emphasis may be used to good advantage herein.

The diversity "receivers referred to herein are described by J. B. Moore in an article appearing in the RCA Review for July 1937 entitled Recent Developments in Diversity Receiving Equipment and also in an article by H. H. Beverage and H. 0. Peterson appearing in the Proceedings of the I. R. E. for April 1931.

In connection with the system of Figure 3, the coupling or the amplification of the signal may be varied so as to produce the desired swing in the sub-carrier frequency. The output of the modulated sub-carrier generators may be limited to the constant value often volts or, more simply, by suitable taps on transformers or resistors the output may be adjusted to the desired constant voltage. Also, in connection with Figure 4 the signal input may be varied or the amplification thereof may be varied so as to produce the desired limit of frequency modulation. The output of the respective sub-carrier generators and v a converter I35 also supplied from an oscillation generator I controlled by crystal I I5 or by any other suitable controlling element such as a resonant line. The variabl frequency beat, either the upper or the lower side band as preferred, is filtered out and amplified in the amplifier H6. The output of amplifier II6, therefore, represents a true frequency modulated sub-carrier wave which in turn is fed into a further converter I26 supplied with still higher frequency waves from high frequency oscillation generator I25. The second beating or heterodyning process occurring in I26 produces upper and lower side bands, the upper one of which representing a true frequency modulated wave is fed throughhigh pass filter 121 and transmission line no to amplifier and/or frequency multiplier and/or limiter I3I, in turn feeding antenna I33 through transmission line I32. The lower side bands resulting from the detection process in detector I28 are fed to a low pass filter I 28 which in turn supplies amplifier and automatic frequency control ling or discriminating circuits I29 of the type described, for example, in Seeley Patent 2,121,103. Should there be a drift in frequencyaway from the channel assigned to the transmitter, the frequency controlling voltages arising across the output of discriminator circuit I29 are fed through lines I22, switch I23 and transmission lines I24 to the high-frequency oscillation generator I25 to vary the frequency thereof in such transmission line I20 into resistor II8 to vary modulators may be limited and by means of transformers or other adjustable couplings the desired voltage may then betaken. off for modulation of the main radio frequency carrier.

In order to maintain signaling on assigned frequencies and within prescribed channels, careful design of circuits to prevent drift should be made and also, as shown in Figures 11 and 12, automatic frequency control may be applied to good advantage. Thus, as applied to a single channel, as shown in Figure 11, the voice or other signal coming in at III is fed through transformer II2 to vary the frequency of a variable frequency high frequency oscillation generator H3. The variable frequency oscillations from II3 are fed into the frequency of oscillation of the variable frequency oscillation generator I I3.

Also, the variable frequency beat from amplifier IIG may be fed to a similar frequency discriminating circuit or automatic frequency controlling circuit II'I for-automatically frequency controlling the oscillation generator II3 to bring the beat frequency of the sub-carrier appearing in the output circuit of amplifier II5 back to the desired sub-carrier frequency channel. 0bviously, all of the automatic frequency controlling systems may be used together or switches I23 and I I9 may be opened, nullifying the A. F. 0. action of circuit I29. On the other hand, switch I23 may be kept closed, switch 9 open and also switch I40 may be left open, in which event only the A. F. C. system I29 will be operative.

As an alternative, I26 may represent a. high frequency oscillation generator which is directly frequency modulated from the sub-carrier waves coming from 6. In this event, filters I28 and I2! would, be identical, each passing the same band of frequencies. Apparatus I25 would represent apparatus for frequency controlling or varying the frequency modulated oscillator I26.

Figure 12 is similar to the transmitting arrangements of Figures 3 and. 4 with. however, automatic frequency control applied. Circuit 200 represents a discriminator circuit of the type described in the Seeley patent referred to above. This circuit is designed to operate with the entire band of sub-carrier frequencies. With switch 202 closed, automatic frequency controlling voltages are applied 'to the frequency variable oscillation generators 6 to I0 inclusive in such a direction as to make the entire band of sub-carrier frequencies stay within its assigned channel.

" Also, part of the output of the transmitting system is fed through lines I to a converter beat frequency amplifier and frequency discriminating circuit 200. The converter fill is also supplied with oscillations from a crystal or other constant frequency oscillation generator 208. The automatic frequency controlling voltages arising in transmission line fill areused to automatically frequency control the frequency modulated oscillator or generator It. If desired, the frequency controlling voltages arising across transmission line Iii may be fed through wires M2 and switch 2 to give a supplemental con-. trol on the whole group of sub-carrier frequency generators through the transmission line I" in addition to the control given by'apparatus I". If desired, switch 202 may be left open and switch 2 closed. r, switch ill may be left open and switch 202 closed. Or, both switches may be closed, as found desirable.

The systems of either Figures 11 or 12 for automatically frequency controlling the transmitting end of the signaling system may be applied also when the sub-carrier generators are phase modulated and the main carrier II or I28 are also phase modulated or when the sub-carriers are frequency modulated and the main carrier phase modulated, or when the sub-carrier frequencies are phase-modulated and the main carrier fre-' quency modulated, or when the sub-carrier frequencies are phase modulated and the main carrier phase modulated, or when the sub-carrier frequencies are amplitude modulated and the cessively higher mean frequency, means for modulating each of the sub-carrier waves generated with a different signal, the sub-carrier waves of higher frequencies being modulated to a greater degree than the sub-carrier waves of lower frequencies, means .for combining the modulated sub-carrier waves, and means for utilizing the combined sub-carrier waves to modulate a main high frequency carrier wave whereby the signal-to-noise ratio in each signal channel is maintained approximately equal.

2. A signaling system comprising means for generating a series of sub-carrier waves of different sub-carrier frequencies, means for angular velocity modulating each of the sub-carriers with a different signal, the sub-carriers of successively higher frequency being angular velocity modulated in successively higher degrees, means for combining the angular velocity modulated subcarriers, and means for utilizing the combined sub-carriers to angular velocity modulate another carrier of a frequency higher than any of the modulated sub-carriers whereby each signal channel has approximately the same signal-tonoise ratio.

3. In a signaling system, means for generating a series of sub-carriers of the same amplitude but of successively higher frequency, means for angular velocity modulating each of the sub-carriers with a different signal, the degree of angular velocity modulation increasing in direct proportion to the frequency of the sub-carrier, means for combining the angular velocity modulated sub-carriers, and means for angular velocity 2,sos,4oa

modulating a wave of still higher frequency than any of the modulated sub-carriers with the combined sub-carriers.

4. In a signaling system a plurality of signal sources, a plurality of sub-carrier generators, the channel width assigned to each sub-carrier generator varying in direct proportion to the frequency of the sub-carrier, means for angular velocity modulating each of the sub-carriers in accordance with'a different signal so as to cause the sub-carrier to fully occupy its assigned channel, combining the modulated sub-carriers and utilizing the combined sub-carriers to angular velocity modulate a carrier of a frequency higher than any of the modulated sub-carriers.

5. In a signaling system, means to generate a series of sub-carrier waves of successively higher frequency, means to angular velocity modulate each of the sub-carriers the same amount, means for adjusting the amplitudes of the modulated sub-carriers to successively higher values in accordance with the frequency of the sub-carriers,

means to combine the modulated sub-carriers, and means to utilize the combined carriers to modulate a main high frequency carrier.

8. In a signaling system, means for generating a main carrier wave,'means for generating a series of sub-carriers, means for modulating the frequency of the main carrier an equal amount by each of the several sub-carriers, and means for frequency modulating the sub-carriers in direct proportion to their sub-carrier frequencies.

7. In a signaling system, means for generating a main carrier frequency, means for generating several sub-carriers, and means for modulating the main carrier by the sub-carriers an amount which increases in proportion to the frequency of the sub-carrier modulating the main carrier.

8. In a signaling system, means for generating a series of sub-carriers, means for generating a main carrier, means for angular velocity modulating the sub-carriers by amounts which are proportional to the square root of the subcarrier frequencies, and means for modulating the main carrier by amounts which are proportional to the square root of the sub-carrier frequencies.

9. In a multiplex system, a plurality of subcarrier generators, means for angular velocity modulating each of the sub-carrier generators with a different signal, means for combining the modulated sub-carriers, means for generating a main high frequency carrier, and means for angular velocity modulating the main carrier with the combined sub-carriers, the modulation adjustment being such that the product of the deviation of each sub-carrier and the deviation of the main carrier produced thereby increases in proportion to the sub-carrier frequency.

10. In a signaling system, means for generating a series of alternating current voltage waves of successively higher frequency, means for impressing a different signal on each of said waves,

means for combining said waves, and means for so utilizing the combined waves to angular velocity modulate a high frequency carrier wave that the degree of angular velocity produced in the high frequency carrier wave increases with the voltage waves of successively higher frequency. 1

11. In a signaling system, means for generating a series of relatively low frequency alternating waves. means for generating a high frequency carrier wave, the relatively low frequency waves being of different frequencies and having impressed thereon different signals, and means for modulating the high frequency carrier wave with said relatively low frequency waves by amounts which are proportional to the square root of the ing waves, means for generating a high frequency carrier wave, the relatively low frequency waves being of different frequencies and having impressed thereon different signals, and means for angular velocity modulating the high frequency carrier wave with said relatively low frequency waves by amounts which are proportional to the square root of the frequencies of said relatively low frequency signal carrying waves.

13. In a signaling system, means for generating a series of relatively low frequency alternating waves, means for generating a high frequency carrier wave, the relatively low frequency waves being of difierent frequencies and having impressed thereon different signals, and means for frequency modulating the high'frequency carrier wave with said relatively low frequency waves by amounts which are proportional to the square root of the frequencies of said relatively low frequency signal carrying waves. r

14. A multiplex system comprising means .for generating a series of sub-carrier radio frequencies of successively higher mean frequency, means for so modulating each of the sub-carriers generated with a different signal that the higher sub-carrier frequencies are modulated to a greater degree than the low sub-carrier frequencies, means for combining the modulated sub-carrier frequencies, and means for utilizing the combined sub-carriers to modulate an ultra high frequency carrier wave. I

15. In a signaling system, means for generating a series of sub-carriers of the same amplitude but of successively higher frequency, means for means for adjusting the amplitudes of the modulated sub-carriers to successively higher values in accordance with-the frequency of the sub-carriers, means to combine the modulated sub-carriers, and means to utilize the combined carriers to angular velocity modulate a main high frequency carrier.

18. In a signaling system, means for generating a series of alternating waves of successively higher frequency, -means for modulating each of the waves with a different signal, and means 1 for so utilizing the modulated waves to frequency modulate a main high frequency carrier that the degree of modulation produced in the main carrier increases with the modulated waves of successively higher frequency.

19. In a signaling system, means for generating a main carrier frequency, meansfor generating several sub-carriers, and means for frequency modulating the main carrier an amount which increases in proportion to the frequency of the sub-carrier modulating the main carrier.

20. In a signaling system, means for generating a series of sub-carriers, means for generatfrequency modulating each of the sub-carriers with a diflerent signal, the degree of frequency modulation increasing in direct proportion to the frequency of the sub-carrier, means for combining the frequency modulated sub-carriers,

and means for angular velocity modulating a wave of still higher frequency than any of the modulated sub-carriers and means for transmitting said last-named wave of still higher frequency than any of the modulated sub-carriers.

16. In a signaling system a plurality of signal sources, a plurality of sub-carrier generators, the channel width assigned to each sub-carrier generator varying in direct proportion to the frequency of the sub-carrier, means for angular velocity modulating each of the sub-carriers in accordance with a different signal so as to cause the sub-carrier to fully occupy its assigned channel, means for combining the modulated subcarriers and utilizing the combined sub-carriers to modulate in frequency an ultra high frequency carrier and means for transmitting said modulated ultra high frequency wave. 7,

1'1. In a signal ing system, means to generate a series of sub-carrier waves of successively higher frequency, means to modulate each of the ing a main carrier, means for modulating in frequency the sub-carriers by amounts which are proportionalto the square root of the sub-carrier frequencies, and means for modulating the main carrier by amounts which are proportional to the square root of the sub-carrier frequencies.

21. In a signaling system, means for generating a series of sub-carriers of successively higher frequency, means for modulating each of the subcarriers with a different signal, and means for so utilizing the modulated sub-carriers to frequency modulate a main carrier that the degree of frequency modulation produced in the main carrier increases with the successively higher sub-carrier frequencies.

22. In a signaling system, means for generating a main ultra high frequency carrier wave, means for generating a series of low frequency sub-carriers, means for-modulating the frequency of the main carrier an equal amount by each of the several sub-carriers, and means for 'fregenerator being assigned to each signaling chan-- nel, means for angular velocity modulating the waves. generated by said sub-carrier generators with different signals, means combining the modulated sub-carrier waves, a high frequency carrier generator, and means for angular velocity modulating the carrier wave generated. by said high frequency carrier generator with said combined sub-carrier waves, the deviation of the generated waves being adjusted so that for each channel the product of the deviation produced in a sub-carrier wave and of the deviation of the main carrier by the sub-carrier of said given channel increases in proportion to the sub-carrier frequency.

HAROLD O. PETERSON. 

